A method for reducing biological contamination of indoor air, which method includes providing a concentrated salt solution, which is either (i) a brine capable of responding to aeration thereof by a rapid increase of its Redox potential, wherein the rate of said increase is greater than the rate of increase observed for a 45% (w/w) calcium chloride solution subjected to identical aeration conditions or (ii) a brine which is passed through an electrolytic cell in order to raise its Redox potential circulating said concentrated salt solution through a treatment zone causing a stream of biologically contaminated air to flow through said treatment zone, such that said contaminated air is contacted with said salt solution in said treatment zone and withdrawing purified air from said treatment zone.
